Cyber Resilience

CVE-2026-8958

Mozilla Firefox ≤ 140.11.0

Published
19 May 2026
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 8.6
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
EPSS Score 0.0034 27th percentile
Risk Priority 61 floored blend · peak EPSS

Summary

CVE-2026-8958 is a high-severity Exposure of Resource to Wrong Sphere (CWE-668) vulnerability in Mozilla Firefox. Its CVSS base score is 8.6 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Abuse Elevation Control Mechanism (T1548); ranked at the 27th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access ControlA06:2025 Insecure Design

EU & UK References

Vulnerability Data

Information disclosure, sandbox escape in the Security: Process Sandboxing component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

CWE(s)
CWE-668CWE-693

Related Threats

MITRE ATT&CK Enterprise Techniques

T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1552.005 Cloud Instance Metadata API Credential Access
Adversaries may attempt to access the Cloud Instance Metadata API to collect credentials and other sensitive data.
attack.mitre.org →
T1552.007 Container API Credential Access
Adversaries may gather credentials via APIs within a containers environment.
attack.mitre.org →
T1553 Subvert Trust Controls Defense Impairment
Adversaries may undermine security controls that will either warn users of untrusted activity or prevent execution of untrusted programs.
attack.mitre.org →
T1553.005 Mark-of-the-Web Bypass Defense Impairment
Adversaries may abuse specific file formats to subvert Mark-of-the-Web (MOTW) controls.
attack.mitre.org →
T1600 Weaken Encryption Defense Impairment
Adversaries may compromise a network device’s encryption capability in order to bypass encryption that would otherwise protect data communications.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-6763Same product: Mozilla Firefox
CVE-2025-10528Same product: Mozilla Firefox
CVE-2026-16377Same product: Mozilla Firefox
CVE-2026-16370Same product: Mozilla Firefox
CVE-2026-16383Same product: Mozilla Firefox
CVE-2026-6774Same product: Mozilla Firefox
CVE-2026-12316Same product: Mozilla Firefox
CVE-2026-16390Same product: Mozilla Firefox
CVE-2026-16388Same product: Mozilla Firefox
CVE-2026-2761Same product: Mozilla Firefox

Affected Assets

mozilla
firefox
≤ 140.11.0 · ≤ 151.0.0
mozilla
thunderbird
≤ 140.11 · ≤ 151.0.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 16 hardening rules · 7 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V6.3.3
  • V6.6.3
  • V10.2.2

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Access enforcement directly stops resources from being reachable by actors outside the intended control sphere.

AC-4 Information Flow Enforcement good match

AC-4 mandates use of information flow enforcement mechanisms to control data movement.

SC-2 Separation of System and User Functionality good match

SC-2 requires separation of user and system functionality as a protection mechanism.

SC-28 Protection of Information at Rest good match

SC-28 requires protection mechanisms for information at rest.

SC-3 Security Function Isolation good match

SC-3 requires isolation of security functions from non-security functions.

SC-7 Boundary Protection good match

SC-7 requires boundary protection mechanisms to monitor and control external communications.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-03 mostly match
prevents

Enforcing authentication directly implements a core protection mechanism whose absence or misuse is the CWE.

PR.AA-05 mostly match
prevents

Enforcing least-privilege authorizations directly prevents resources from being exposed outside their intended control sphere.

PR.DS-01 mostly match
prevents

Cryptographic and integrity controls are protection mechanisms whose correct deployment mitigates the CWE.

PR.DS-02 mostly match
prevents

Encryption and integrity protections for transit are explicit protection mechanisms.

PR.IR-01 mostly match
prevents

Logical network protections are protection mechanisms whose failure matches the CWE.

PR.PS-01 partial match
prevents

Hardened configuration baselines ensure protection mechanisms are correctly applied and maintained.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.36 Compliance with policies, rules and standards for information security partial match
finds

Systematic verification that security mechanisms operate according to defined standards reduces the likelihood that protection mechanisms are bypassed or disabled.

A.8.20 Networks security partial match
mitigates

Hardening devices, disabling vulnerable protocols, and maintaining accurate network diagrams reduce the likelihood that a protection mechanism is misconfigured or left in a weak state.

A.8.22 Segregation of networks partial match
mitigates

Placing systems of differing trust levels into separate domains prevents resources from being placed in a sphere where they are reachable by unintended actors.

A.5.24 Information security incident management planning and preparation none match
none

Requiring defined escalation paths, crisis activation criteria, and coordination procedures strengthens the overall protection mechanism so that a single control failure is less likely to leave the organization exposed.

A.5.25 Assessment and decision on information security events none match
none

By requiring a documented categorization and decision process for security events, the control ensures that protection mechanisms are not bypassed or ignored when anomalies occur.

A.5.26 Response to information security incidents none match
none

Identifying and remediating control weaknesses that contributed to an incident reduces the likelihood that protection mechanisms will fail again.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (4 rules)
  • V-248524 OL 8 must implement NIST FIPS-validated cryptography for the following: To provision digital signatures, to generate cryptographic hashes, and to protect data requiring data-at-rest protections in accordance with applicable federal laws, Executive Orders, directives, policies, regulations, and standards. prevents CWE-693
  • V-248525 All OL 8 local disk partitions must implement cryptographic mechanisms to prevent unauthorized disclosure or modification of all information that requires at-rest protection. prevents CWE-693
  • V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-668
RHEL 7 (1 rule)
  • V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-668
Windows 10 (3 rules)
  • V-220865 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
  • V-220812 Credential Guard must be running on Windows 10 domain-joined systems. prevents CWE-693
  • V-220967 The Debug programs user right must only be assigned to the Administrators group. prevents CWE-668
Windows 11 (2 rules)
  • V-253490 The "Debug programs" user right must only be assigned to the Administrators group. prevents CWE-668
  • V-253418 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-693
Windows Server 2016 (2 rules)
  • V-225012 Windows Server 2016 must be running Credential Guard on domain-joined member servers. prevents CWE-693
  • V-225079 The Debug programs user right must only be assigned to the Administrators group. prevents CWE-668
Windows Server 2019 (2 rules)
  • V-205757 Windows Server 2019 Debug programs: user right must only be assigned to the Administrators group. prevents CWE-668
  • V-205907 Windows Server 2019 must be running Credential Guard on domain-joined member servers. prevents CWE-693
Windows Server 2022 (2 rules)
  • V-254441 Windows Server 2022 must be running Credential Guard on domain-joined member servers. prevents CWE-693
  • V-254500 Windows Server 2022 debug programs user right must only be assigned to the Administrators group. prevents CWE-668

References